Device for protecting threadings and butt-type joint bearing surfaces of metallic tubes

ABSTRACT

A device for protecting, before use, threadings and butt-type joint bearing surfaces (66) which contribute to the hermetic character and to the threadings (55) of male or female joining regions of metallic tubes. 
     It comprises a ring (56) of plastics material which is screwed onto the threading (55) of the metallic tube (54). A first lip (63) rests in a resilient tight manner on the joint bearing surface (66) in the vicinity of the inner edge (65) thereof. A closed annular volume (67) protects the bearing surface of the joint. A second lip (59) protects the threaded region. 
     This device is used in particular for the frustoconical joint bearing surfaces of tubes with a frustoconical threading. The ring can be clothed by a metallic reinforcing sleeve (68).

The device which is the subject of this invention relates to theprotection, before use, of threadings and butt-type joint bearingsurfaces which make-up threaded couplings between metallic tubes ofcircular cross-section and which contribute to the hermetic character ofthese couplings. This device relates to the threaded couplings ofmetallic tubes which are connected to each other in a direct manner orby means of threaded couplings or sleeves.

This device relates in particular to the protection of butt-type jointbearing surfaces and threadings of tubes used for the drilling of oilwells, or for the exploitation (tubing) of these wells, or even for thecasing of these wells.

The threaded coupling described in FR No. 1 489 013 in particular isknown among the different types of threaded couplings which have beendeveloped. The butt-type joint bearing surface which should ensure thehermetic character of the joint has a concave frustoconical annularsurface, worked at the male end of a tube, which comes to a stop againsta convex frustoconical annular surface which is worked in the vicinityof the inner end of the female threading.

The hermetic character of the coupling depends on the quality of thethreadings and the butt-type joint bearing surfaces, a quality which canbe deteriorated either by impact, during transportation for example, orby corrosion, particularly on contact with salt water or otheraggressive media.

Different devices have been proposed for protecting the joining regionsof threaded tubes.

Patent Application DE-OS No. 2 834 489 describes an elastomeric orplastics protective cover which covers the outer threading of a tube.Inner raised regions, which are substantially parallel to the axis,ensure that the cover is held on the threads. The device can also beadapted to protect an inner threading.

This device is not intended for the protection of joint bearing surfacesand, not having a hermetic character, does not protect againstcorrosion.

Utility model DE-GBM No. 7 800 484.9 describes a protecting device formale or female frustoconical threadings at the ends of steel tubes,comprising a component of flexible material, such as an elastomer, towhich there is connected a tubular reinforcing section of steel. Thecomponent of flexible material is provided with a frustoconicalthreading which threadingly engages the steel tube and comprises twosealing joints, one of which engages with the front end of the tube.

Such a device does not enable the butt-type joint bearing surfaces, suchas the frustoconical bearing surfaces described in FR No. 1 489 013, tobe effectively protected. Indeed, it is difficult to screw correctly thethreads of a flexible material and it is difficult to control the tightcompression of the joint onto the abutment regions. Finally, theflexibility of the material means that its protecting function withrespect to the impacts received in the regions not covered by thereinforcing section, is poor.

Patent Application GB No. 2 093 426 describes a cover for protecting theouter tube threading. It comprises an outer sheath, preferably of steel,and an inner wall, preferably of impact-resistant plastics material. Theinner wall is threaded so that it screws onto the outside of the tube.The extreme edge of the tube is protected by a rounded rim of the coverwhich covers it.

This device is not designed to protect the butt-type joint bearingsurfaces, such as the frustoconical bearing surface against corrosion.Moreover, it does not have any means for ensuring protection againstcorrosion of the region covered by the cover. Finally it can not be usedfor the protection of the inner threadings of tubes.

A study has been made of producing a device which can ensure theeffective protection against corrosion and impacts, before use, ofthreadings and butt-type joint bearing surfaces, which make-up threadedcouplings of metallic tubes. A study in particular has been made of thepossibility of protecting the inner or outer threadings and thebutt-type joint bearing surfaces, such as those described, for examplein Patent No. FR 1 489 013.

A study has also been made of the possibility of maintaining a certainvolume of a protective fluid in contact with the butt-type joint bearingsurfaces.

Finally, a study has been made of the possibility of producing aprotecting device which is simple to assemble and disassemble, which isresistant to impacts and vibratons and permits, if required, the freepassage inside the metallic tube of tools or measuring instruments,without disassembly.

The device for protecting the threaded couplings of metallic tubes whichis the subject of the present invention allows this problem to be solvedin a particularly simple and advantageous manner. This device relates tothe protection of the threadings and butt-type joint bearing surfaces ofmetallic tubes and particularly the butt-type joint bearing surfaceswith frustoconical surfaces described in FR No. 1 489 013.

This device comprises a ring of rigid plastics material, furnished witha threading which engages, by screwing, into the male or femalethreading of the joining region, furnished with a butt-type jointbearing surface, of a metallic tube or tubular coupling. This ringcomprises an annular abutment region the front face of which ispositioned so that it faces the joint bearing surface of the metallictube when the ring is tightly screwed onto the tube. The inner edge ofthis front face is equiped with a first annular sealing means whichco-operates with the joint bearing surface of the tube, in the vicinityof the inner edge thereof, to ensure an hermetic character. The profileof this front face is produced by taking into account the profile of thejoint bearing surface of the tube so as to delimit an annular volumebetween this front face and the joint bearing surface which is closedowing to the tight bearing provided in the vicinity of the inner edgesof this front face and this joint bearing surface.

This closed annular volume is advantageously filled, at least partially,with a fluid, such as a lubricant, which protects the joint bearingsurface, particularly against corrosion.

The ring may also have a second annular sealing means, whose action iscombined with that of the first. This second means is arranged so thatit forms a tight bearing against the metallic tube, when the ring isscrewed tightly, in the vicinity of one end of its threading, thebutt-type joint bearing surface being located in the vicinity of theother end of this same threading. The first annular sealing means isadvantageously a lip formed by the inner edge of the front face of thering. The second sealing means can also be an annular lip, integral withthe ring, the profile of which is such that it is in contactof anhermetic type with the wall of the tube when the ring is screwed ontightly. This second tight sealing means can also be an inserted joint,such as an 0-ring joint, accommodated, for example, in an annularhousing provided in the ring.

The region of the ring facing the threading of the metallic tube, whenit is screwed on tightly, can have only several threads, the remainderof the surface being smooth.

The ring advantageously is also furnished with a rear region whichextends beyond the end of the tube when it is screwed on tightly. Thisregion can be equiped with holding means, such as projections whichfacilitate the holding of screwing or unscrewing instruments. Theseprojections which are preferably parallel to the axis, are arranged onthe inner and/or outer wall of the ring.

The main part of the surface of the ring, can be clothed, on theunthreaded side, with a metallic sleeve, which is made integral with thering by any suitable means, to increase the impact-resistance of thering. This sleeve can extend beyond the end of the plastic ring in thedirection away from the metallic tube. This sleeve can then be adaptedso that it has a region equiped with holding means, such as projectionswhich facilitate the holding of screwing or unscrewing instruments.

The inner diameter of the plastics ring, whether clothed or not with ametallic sleeve, is such that it permits the free passage of tools ormeasuring instruments, without the protecting device having to beunscrewed. Alternatively, for certain applications, the protectingdevice can be closed by a sealing circular bottom, integral with thering of plastics material or with the sleeve with which it can beclothed. This circular bottom can be removable.

A plastics material with good hardness and elasticity characteristics,such as a polyurethane-based material, is advantageously used to producethe ring. A plastics material which also has very good impactresistance, particularly at low temperature, is advantageously usedparticularly when the ring is not clothed with a metallic sleeve.Modified polyamides, for example or certain polyethylene qualities canbe used to provide increased impact resistance.

The metallic sleeve with which the ring can be clothed is made-up of asuitable metal or alloy, such as ordinary, alloyed or stainless steel.

The device according to the invention is suitable, more particularly,for protecting the joining regions of metallic tubes with frustoconicalmale or female threadings. The ring then has corresponding threadings,preferably limited to a few threads. The centering of the ring beforescrewing is thereby facilitated, the jamming by superposition of threadsis avoided and the screwing and unscrewing time is reduced. Finally theinvention relates to the plastics ring itself, whether clothed or notwith a metallic sleeve, which enables the device according to theinvention to be produced.

The following description and Figures allow a better understanding in anon-limited manner, of the main characteristics of the protecting deviceaccording to the invention, as well as the advantageous characteristicsof particular embodiments of this device.

FIG. 1 is an axial half-section of a protecting device according to theinvention made up of a ring of plastics material screwed onto the maleend of a metallic tube.

FIG. 2 is an enlarged view of part of FIG. (1) showing the position ofthe second sealing means, with which the ring of plastics material isprovided.

FIG. 3 is an axial half-section of a protecting device according to theinvention made up of a plastics ring screwed onto the female end of ametallic tube.

FIG. 4 is an axial half-section of a protecting device according to theinvention made up of a plastics ring, clothed with a metallic sleeve,screwed onto the male end of a metallic tube.

FIG. 5 is an axial half-section of a protecting device according to theinvention made up of a plastics ring, clothed with a metallic sleeve,screwed onto the female end of a metallic tube.

FIG. 6 is an end view, along arrow F, of the extended section of themetallic sleeve shown in FIG. 5.

FIG. 1 shows, in an axial half-section, a metallic tube (1) of circularcross-section with axis (X₁ -X₂), the male joining region (2) of whichis protected by a device according to the invention. This joining regionhas an outer frustoconical threading (3) and a concave butt-typefrustoconical joint bearing surface (4), the generating line of which isinclined by from about 15° to 25° with respect to a plane perpendicularto (X₁ -X₂). The bearing surface (4) is connected to the end of thethreading (3) by a chamfer (5).

The protecting device comprises a one-piece ring (6) of plasticsmaterial provided with an inner threading (7) having only a few threads,which is screwed tightly onto the threading (3) of the tube until it hasbeen screwed to a stop. The abutment region (8) of the ring has anannular front region (9) facing the bearing surface (4) of the joint.The inner edge of this front face has a first annular sealing means,formed by the lip (10) which, owing to the screwing of the ring onto thetube, forms a tight bearing on the bearing surface of the joint, in thevicinity of the inner edge (4A) of this bearing surface. It can beobserved that, in the embodiment of the device according to theinvention shown in FIG. 1, the annular lip (10) oriented towards theinside of the tube is engaged inside the circle formed by the inner edge(4A) of the bearing surface (4). The outer edge (10A) of the lip (10)therefore faces the inner wall of the tube (1) in the connection region(4B) to the inner edge (4A) of the joint bearing surface (4), when thering is screwed on tightly. Under these conditions, the inner edge (4A)bears against the front face (9) in the connection region between theouter edge (10A) of the lip (10) and the section of the front face whichfaces the bearing surface of the joint (4). A closed annular volume (11)is enclosed between this front face and this bearing surface of thejoint. This volume, of a substantially triangular cross-section in thisFigure, is preferably filled with a protecting fluid, such as alubricant. It can be observed that, due to the particular arrangement ofthe lip (10) shown in the Figure, the bearing surface (4) of the jointis protected by the protecting fluid contained in the closed annularvolume (11) over the entire surface thereof. Moreover, the projection ofthe lip (10), in a direction substantially parallel to the axis, towardsthe inside of the tube, forms a sort of labyrinth which limits thelosses of protecting fluid wherever there is a loss of sealing at thelevel of the contact between the inner edge (4A) of the bearing surface(4) and the front face (9) of the abutment region (8) of the ring (6).

The ring can have a second sealing means situated beyond the threadingregion (3) with respect to the bearing surface (4) of the joint toimprove the sealing of this closed space, and also to protect thethreading region. This second means is shown in an enlarged manner inFIG. 2 which is a detail of FIG. 1. It shows the introduction region(12) of the ring (6) around the tube (1). It can be seen that in thevicinity of the introduction edge (13) of the ring (6), a lip (14) isprovided oriented radially towards the axis (X₁ -X₂) which rests on theouter wall of the tube. This lip forms the second sealing means. Thedimensions thereof are such that when the ring is screwed on tightly, itrests tightly and resiliently on the outer wall of the tube. Thepenetration of corrosive fluids between the ring and the tube, in thedirection of the threading (3) and the closed volume (11) is therebyprevented. The minimum inner diameter (D₁) of the ring is greater thanthe inner diameter (D₂) of the tube in a running section, therebypermitting the passage of tools and measuring instruments. The region(15) of the ring which extends beyond the end of the tube hasprojections, such as (16,17), formed on the outer and inner wallsrespectively. These projections are substantially parallel to the axisand permit the holding of instruments for screwing or unscrewing. Thethickness of the ring is determined such that the ring withstands theimpacts caused by handling of the tube and effectively protects the endregion thereof. Thus an extra thickness (18) is provided in the vicinityof the introduction region (12) of the ring which may be subjected tosubstantial stresses and impacts. This extra thickness enables inparticular impacts perpendicular to the axis X₁ -X₂ to be absorbed.

FIG. 3 shows, as an axial half-section, the protecting device accordingto the invention mounted on the end of a rotatory metallic tube (19),with axis (X₃ -X₄), to protect the female joining region (20) thereof.This region comprises an inner frustoconical threading (21) and a convexbutt-type frustoconical joint bearing surface (22). This tube can alsobe a coupling or sleeve used to assemble tubes having joining regionswith a male frustoconical threading.

The generating line of the joint bearing surface (22) is inclined byfrom 15° to 25° with respect to a plane which is perpendicular to theaxis (X₃ -X₄). This joint bearing surface is connected to the end of thethreading region of the tube by a chamfer (24).

The protecting device comprises a single-piece ring (25) of plasticsmaterial, provided with an outer threading (26) having only severalthreads, which is screwed tightly onto the inner threading of the tubeuntil it is screwed to a stop. The abutment region (27) of the ring hasa frontface (28) facing the joint bearing surface (22).

As in FIG. 1, the annular lip (29), oriented towards the inside of thetube (19) is engaged inside the circle formed by the inner edge (22A) ofthe joint bearing surface (22). This inner edge (22A) is located at theintersection of the bearing surface (22) and the inner wall (23) of thetube (19).

When the ring is screwed on tightly, as shown in the Figure, this inneredge (22A) rests against the front face (28) in the connection regionbetween the outer edge (29A) of the lip (29) and the section of thisfront face (28) which faces the bearing surface (22) of the joint. Thegenerating line of this section of the front face is inclined withrespect to that of the bearing surface of the joint so as to set aside aclosed annular volume (30) which may be filled with a protecting fluid,such as a lubricant. The projection of the lip (29) towards the insideof the tube (19) forms a sort of labyrinth, limiting the losses ofprotecting fluid, and thereby the risk of penetration of corrosivefluids, where a loss of sealing is produced at the level of the contactbetween the inner edge (22A) of the joint bearing surface (22) and thefront face (28).

To complete the protection, particularly with regard to the threading(21) of the tube (20), a second sealing means is provided beyond thisthreading, with respect to the bearing surface (22) of the joint,between the ring and the end region(31) of the tube. This second meansis an annular lip (32), attached at a break in contact (33) of thereinforced rear wall (34) of the ring (25), which resiliently andtightly rests on the end face (35) of the tube (20). The dimensions ofthe ring (25) are determined so that, when it is screwed on tightly,tight contacts are simultaneously produced at the level of the first andthe second sealing means. The threading (21) and the closed volume (30)are thus protected, in a particularly effective manner, against thepenetration of corrosive fluids, such as sea water.

The reinforced annular region (34) of the ring permits the end region(31) and the face (35) of the tube to be protected from impact. Thisreinforced region (34) has projections, such as (36, 37) provided on theouter wall and the inner wall respectively, which permit the holding ofscrewing or unscrewing instruments. The minimum inner diameter (D₃) ofthe ring is slightly less than the inner diameter (D₄) of the tube in arunning section so as to permit the passage of tools or calibratinginstruments of conventional types.

FIGS. 4 to 6 show an embodiment of the device according to the inventionin which the plastics ring is clothed by a metallic sleeve to increasethe impact-resistance thereof.

FIG. 4 shows, as an axial half-section, a particular embodiment of aprotecting device (38) according to the invention, provided about theend of a metallic tube (39), with axis X₅ X₆, provided with a malefrustoconical threading (40) and, at the end, with a concave butt-typefrustoconical joint bearing surface (41). This device comprises aplastics ring (42) having only a few threads (43).

The entire inlet region (44) of this ring, over more than half of thefrustoconical bearing surface, is smooth. This ring is shown screwedtightly onto the tube.

A small annular lip (45) rests on the outer cylindrical wall (46) of themetallic tube (39) at the end in front of the inlet region (44) of thering (42). It forms the second sealing means. The ring (42) has,moreover, an abutment region (47), whose lip (48), which forms the inneredge of the front face (49), rests on the inner edge (50) of the bearingsurface (41) of the joint. This lip (48) forms the first sealing means.A closed annular volume (52) is thereby formed between the bearingsurface (41) and the front face (49).

The ring (42) is clothed on its outer wall by a metallic sleeve (51)which extends beyond the end of the ring, beyond the end of the tube andthereby protects the tube from localised impacts. This sleeve can, forexample, be of mild steel. It is advantageous to provide as solid aconnection as possible between the ring and the sleeve. For thispurpose, it is possible in particular to use the sleeve as one of thewalls of a mould, inside which the ring of plastics material is shaped.Moreover, projections and/or cavities on which the plastics materialcatches can also be provided on the inner wall of the sleeve (51). Otherconnecting means can also be provided.

FIG. 5 shows, as an axial half-section, a protecting device (53)according to the invention, provided on the end of a metallic tube (54),with axis of revolution X₇ X₈, provided with a female frustoconicalthreading (55). The plastics ring (56) has a few threads (57) at the endhaving the large diameter of the region of engagement at the end of thetube (54). An annular lip (59) formed on the rear flange (60) of thering rests on the front edge (61) of the tube (54).

An abutment region (62) is provided at the end in front of the ring(56). As in the case of FIG. 3, an annular lip (63), oriented towardsthe inside of the tube (54), is engaged inside the circle formed by theinner edge (65) of the butt-type joint bearing surface (66). This inneredge (65) is at the intersection of the joint bearing surface (66) andthe inner wall (66A) of the tube (54). When the ring is screwed ontightly, as is the case in the Figure, the inner edge (65) rests againstthe front face (64) in the joining region between the edge (63A) of thelip (63) and the section of the front face (64) facing the joint bearingsurface (66). The generating line of this front face is inclined withrespect to that of the joint bearing surface thereby forming a closedannular volume (67) which may be filled with a protecting fluid, such asa lubricant. The projection of the lip (63) towards the inside of thetube (54) forms a sort of labyrinth which limits the losses ofprotecting fluid and thereby the risk of penetration of corrosivefluids, particularly in the case where a loss of sealing is produced atthe level of the contact between the inner edge (65) and the front face(64).

The lip (59) which forms the second sealing means furthermore improvesthe protection of the entire space between the ring (56) and the tube(54), thereby avoiding in particular the corrosion of the threading ofthe tube by the penetration of moisture.

A sleeve (68) is made integral with the ring (56) in the manner alreadydescribed above. The extended section (69) with a greater diameter isconnected to the section covered by the ring (56) by a fillet (70). Thisallows impacts received from outside to be withstood. Moreover, as shownby FIG. 6, which is a view, seen along arrow F, of the end region of thesleeve, two noses (71,72), parallel to the generating lines, formingprojections inside, are provided on the extended section (69) of thesleeve (68). They permit the end (73), seen in cross-section, of arotating tool, not shown, to be introduced into this extended section.

The protecting device (53) can thereby be assembled and diassembled veryrapidly, the rotating tool (73) driving therotation of the sleeve due tothe noses (71 and 72).

For certain applications, the ring (6, 25, 42), may have, in thevicinity of its rear end for example, a solid circular wall which closesin a hermetic manner, the way through the ring and therefore the inletof the metallic tube onto which it is screwed. In the case of the ringbeing clothed by a metallic sleeve (51, 68) this solid circular wall canbe integral with the sleeve itself. This circular wall can also beremoved.

Numerous modifications can be made to the device according to theinvention without exceeding the scope thereof. It is possible, as shownby FIG. 4, to use, as the first sealing means, a lip, which instead ofbeing engaged inside the circle formed by the inner edge of the bearingsurface of the joint, faces this bearing surface in the vicinity of theinner edge. An 0-ring joint or another type of joint can be used as asecond annular sealing means.

I claim:
 1. A device for protecting male or female threadings andbutt-type annular joint bearings of metallic tubes comprising:a metallictube provided with a joining region at one end thereof, said joiningregion including screw threadings which terminate in a butt-type jointhaving a butt-type bearing surface and inside and outside surfaces wheresaid bearing surface and said inside surface meet to form an annularinner edge, a plastic ring provided with screwthreads for engaging saidthreadings of said metallic tube, said ring further having an annularabutment region provided with a front face which is dimensioned so as toface the butt-type bearing surface of the metallic tube when the ring istightly screwed onto said tube, said front face having an inner surfacewhich comprises a first annular tight sealing means which cooperateswith the butt-type joint bearing surface near said annular inner edge toinsure sealing, said front face being further dimensioned such that aclosed annular volume is created between the entire butt-type jointbearing surface and said front face.
 2. A device according to claim 1,wherein the first annular sealing means is a lip oriented toward theinside of the metallic tube and which, when the ring is tightly screwedon, is engaged inside a circle formed by the inner edge of the butt-typejoint bearing surface in such a manner that the lip at its outer edgefaces the inside surface of the tube.
 3. A device according to claim 2,wherein the inner edge of the butt-type joint bearing surface is incontact with the front face of the annular abutment region of the ringbetween the outer edge of the lip and a section of the front face whichfaces the bearing surface of the joint.
 4. A device according to one ofclaims 1 to 3, wherein the ring includes a second annular sealing meanswhich, when the ring is tightened, rests against the metallic tubebeyond one of the ends of its threading, the butt-type joint bearingsurface being at the other end of this threading.
 5. A device accordingto claim 1, wherein the closed annular volume is at least partiallyfilled with a protecting fluid.
 6. A device according to claim 1,wherein a metallic sleeve is made integral with the ring on itsnon-threaded side.
 7. A device according to claim 6, wherein the ringand/or the metallic sleeve extend beyond the end of the metallic tube.8. A device according to claim 7, wherein the portion of the ring or themetallic sleeve which extends beyond the end of the metallic tube isprovided with holding means to permit the holding of instruments forscrewing or unscrewing.
 9. A device according to claim 1, wherein acircular wall closes the inlet of the metallic tube.
 10. A deviceaccording to claim 1, wherein the ring is of polyurethane, polyamide orpolyethylene material.
 11. A device according to claim 1, in which saidfront face of said annular abutment region is inclined with respect tothe bearing surface of the butt-type joint.
 12. A device according toclaim 11, wherein the cross-section of said closed annular volume issubstantially triangular.